Method of preventing complete extrusion of a billet during hydrostatic extrusion

ABSTRACT

In order to prevent the complete extrusion of a billet during hydrostatic extrusion, the rear end of the billet is treated so that it is harder than the rest of the billet. As a result, when the rear end reaches a die, the resistance to extrusion increases and can be detected so that extrusion can be stopped.

United States Paten [191 [111 3,7513% Stromblad Aug. M, 1973 [54] METHOIT ()F PREVENTING COMPLETE 3,455,134 7/1969 Thompson 72/60 sxrnusror: OF A BILLET DURING 3618-351 11/ 1971 HYDROSTATIC EXTRUSION [75] Inventor: llngemar Stromblad, Vasteras,

Sweden [73] Assignee: Allmanna Svenska Elektriska Aktlebolaget, Vasteras, Sweden [22] Filed: Feb. 16, 1972 [2]] Appl. No.: 226,719

[30] Foreign Application Priority Data Marf30, 1971 Sweden 4087/71 [52] [1.8. CI. 72/60 [51] Int. Cl. B2lc 31/00 [58] Field of Search 72/60, 271

[56] References Cited UNITED STATES PATENTS 3,392,562 7/l968 Fuchs, Jr. 72/60 Thompson 72/60 FOREIGN PATENTS OR APPLICATIONS 3,287 2/l967 Japan 72/60 Primary Examiner-Richard .I. Herbst Attorney-Jennings Bailey, Jr.

[5 7] ABSTRACT In order to prevent the complete extrusion of a billet during hydrostatic extrusion, the rear end of the billet is treated so that it is harder than the rest of the billet. As a result, when the rear end reaches a die, the resistance to extrusion increases and can be detected so that extrusion can be stopped.

3 Claims, 2 Drawing Figures PATENTEUAUG x 4:915

k bar BACKGROUND OF THE INVENTION Field of the Invention The Prior Art The present invention relates to a method in hydrostatic extrusion of preventing a billet which is being extruded from being completely extruded through the die opening.

During hydrostatic extrusion a billet is placed in a pressure chamber and subjected to an all-sided pressure by a pressure medium surrounding the billet. Due to the influence of this pressure the billet is forced out through an opening in a die arranged in the pressure chamber.

Extremely high pressure is used during hydrostatic extrusion, normally between and 30 kbars. If a billet is extruded completely, there is an almost explosive outflow of the compressed pressure medium through the opening in the die. The pressure medium being expelled may cause damage to both personnel and the material of the press as well as the extruded product and the surroundings. The extrusion is therefore discontinued before the whole billet has been used. The remnants of the billet are usually scrapped. In order to decrease the waste and exploit the extrusion equipment to the full it is desirable to discontinue the extrusion at the last minute so that the unextruded part of the billet is small. There are various ways of achieving this. For instance, the movement of a pressure-generating plunger is measured. Either the whole movement is measured or the movement from the moment when extrusion of the material through the die starts. The movement is discontinued when it is calculated that the desired volume has been extruded. The first method is very unreliable and the second method, described in US. Pat. No. 3,592,032, in many cases gives reliable results. Another known method of discontinuing the extrusion process is to give the rear part of the billet a larger cross section than the rest of the billet so that the extrusion ratio is altered when this rear part of the billet enters the die. The increased extrusion ratio causes an increase in the pressure required so that the pressure in the pressure chamber increases. This pressure increase is indicated and used to discontinue theextrusion process.

SUMMARY OF THE INVENTION According to the invention a pressure increase which can be indicated is effected in the pressure chamber when the rear part of the billet enters the entrance of the die, the rear part of the billet being treated in such a way that it becomes harder than the rest of the billet. The method is particularly suitable when extruding steel, in which case the rear part of the billet is tempered to a suitable degree of hardness.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be further described with reference to the accompanying drawings.

FIG. I shows the relationship between the extrusion ratio and the extrusion pressure for one and the same material in soft-annealed and heat-treated or tempered state, respectively.

FIG. 2 shows schematically the pressure chamber in a hydrostatic extrusion press.

' DESCRIPTION OF THE PREFERRED EMBODIMENTS The relationship between the required pressure and the extrusion ratio for a type of steel and a copper alloy is shown in FIG. 1. The extrusion ratio is the ratio between the area A ofa billet and the area A of a product produced. The extrusion ratio is therefore A /A. The ratio between the pressure P and the extrusion ratio A,,/A is P= k +k log (A /A) where k and k are constants depending on the material. The curves drawn in the figure refer to the same steel or copper material, respectively, but treated to different degress of hardness.

In FIG. 2, l designates a high pressure cylinder in which a die 2 and a pressure-generating plunger 3 are arranged. In the cylinder are seals 4 and 5 which seal between the cylinder 1 and the plunger 3 and die 2 respectively. The seals fit in grooves formed between the spacer tube 6 and the end closures 7 and 8. The die rests against the table 9 in a press stand not otherwise shown, which also includes an operating cylinder for the pressure-generating plunger 3. In the chamber 10, which is filled with a pressure medium such as castor oil, a billet having a cross section A, is inserted. This billet is shaped in the die to a product 12 having a cross section A. The billet may be a steel for which the relationship between the extrusion ratio and the extrusion pressure in soft-annealed state follows the line Fe, and in hardened state follows the line Fe If the front part b of the billet 11 is soft-annealed material and its rear part a is hardened material, a pressure of about 10 kbars is required for extrusion of the soft-annealed part with an extrusion ratio A,,/A 5. When the hard part a comes into the die a pressure of about 13 kb is required if the extrusion is not to be discontinued, as is seen by the curve Fe,. The pressure increase in the chamber 10 when the hard rear end of the billet reaches the die can be indirectly sensed by a pressure sensing member communicating with the operating cylinder of the pressure-generating plunger. The extrusion can be discontinued by an operating signal from the sensing member when the pressure has reached a predetermined level. Hardening can easily be carried out close to the press with the help of a high frequency unit, which also has the advantage that the risk of the billet being turned the wrong way so that the hard end faces the die is completely eliminated.

The invention can be used for all materials which can acquire varying degrees of hardness by suitable treatment. It is therefore not limited to steel and copper and these materials are only examples.

An important advantage is that the billet has the same cross section along its entire length and that the increase in hardness is effected in the billet material. The increase in cross section necessitated by the previously known method is therefore avoided, which meant upsetting the end of the billet or turning down the greater part of the billet, thus involving considerable losses in material.

Furthermore, the maximum volume of the pressure equipment is utilized, thus giving higher production capacity.

I claim:

1. Method of preventing complete extrusion of a billet during hydrostatic extrusion, which comprises extruding a billet the rear end of which is of harder mateis of steel. rial than the rest of the billet, so that the pressure necessary to extrude the rearmost end of the billet will be higher.

2. Method according to claim 1, in which the billet 5 3. Method according to claim 1, in which the billet is of constant cross-section throughout its length. 

1. Method of preventing complete extrusion of a billet during hydrostatic extrusion, which comprises extruding a billet the rear end of which is of harder material than the rest of the billet, so that the pressure necessary to extrude the rearmost end of the billet will be higher.
 2. Method according to claim 1, in which the billet is of steel.
 3. Method according to claim 1, in which the billet is of constant cross-section throughout its length. 